Micro electro-mechanical system for ejection of fluids

ABSTRACT

An integral structure within an MEMS device is used to filter out foreign bodies in a fluid supply. The system is initially constructed in a large planar form, and the effect of impurities is reduced by fabricating an integral grill structure in the path of the flow of the liquid so as to filter foreign, bodies in the liquid. Ideally used in an ink jet printing system, the grill forms one wall of a nozzle chamber for filtering ink entering the nozzle chamber to be ejected from the nozzle chamber. The filter can be constructed from nitride as is the nozzle chamber.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, US patent applications identified by their US patent application serial numbers (USSN) are listed alongside the Australian applications from which the US patent applications claim the right of priority.

U.S. Pat. No./ PATENT APPLICATION (CLAIMING CROSS-REFERENCED RIGHT OF PRIORITY AUSTRALIAN FROM AUSTRALIAN PROVISIONAL PATENT PROVISIONAL APPLICATION NO. APPLICATION) DOCKET NO. PO7991 09/113,060 ART01 PO8505 09/113,070 ART02 PO7988 09/113,073 ART03 PO9395 09/112,748 ART04 PO8017 09/112,747 ART06 PO8014 09/112,776 ART07 PO8025 09/112,750 ART08 PO8032 09/112,746 ART09 PO7999 09/112,743 ART10 PO7998 09/112,742 ART11 PO8031 09/112,741 ART12 PO8030 09/112,740 ART13 PO7997 09/112,739 ART15 PO7979 09/113,053 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067 ART18 PO7982 09/113,063 ART19 PO7989 09/113,069 ART20 PO8019 09/112,744 ART21 PO7980 09/113,058 ART22 PO8018 09/112,777 ART24 PO7938 09/113,224 ART25 PO8016 09/112,804 ART26 PO8024 09/112,805 ART27 PO7940 09/113,072 ART28 PO7939 09/112,785 ART29 PO8501 09/112,797 ART30 PO8500 09/112,796 ART31 PO7987 09/113,071 ART32 PO8022 09/112,824 ART33 PO8497 09/113,090 ART34 PO8020 09/112,823 ART38 PO8023 09/113,222 ART39 PO8504 09/112,786 ART42 PO8000 09/113,051 ART43 PO7977 09/112,782 ART44 PO7934 09/113,056 ART45 PO7990 09/113,059 ART46 PO8499 09/113,091 ART47 PO8502 09/112,753 ART48 PO7981 09/113,055 ART50 PO7986 09/113,057 ART51 PO7983 09/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54 PO8028 09/112,757 ART56 PO9394 09/112,758 ART57 PO9396 09/113,107 ART58 PO9397 09/112,829 ART59 PO9398 09/112,792 ART60 PO9399 6,106,147 ART61 PO9400 09/112,790 ART62 PO9401 09/112,789 ART63 PO9402 09/112,788 ART64 PO9403 09/112,795 ART65 PO9405 09/112,749 ART66 PP0959 09/112,784 ART68 PP1397 09/112,783 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02 PO8003 09/112,834 Fluid01 PO8005 09/113,103 Fluid02 PO9404 09/113,101 Fluid03 PO8066 09/112,751 IJ01 PO8072 09/112,787 IJ02 PO8040 09/112,802 IJ03 PO8071 09/112,803 IJ04 PO8047 09/113,097 IJ05 PO8035 09/113,099 IJ06 PO8044 09/113,084 IJ07 PO8063 09/113,066 IJ08 PO8057 09/112,778 IJ09 PO8056 09/112,779 IJ10 PO8069 09/113,077 IJ11 PO8049 09/113,061 IJ12 PO8036 09/112,818 IJ13 PO8048 09/112,816 IJ14 PO8070 09/112,772 IJ15 PO8067 09/112,819 IJ16 PO8001 09/112,815 IJ17 PO8038 09/113,096 IJ18 PO8033 09/113,068 IJ19 PO8002 09/113,095 IJ20 PO8068 09/112,808 IJ21 PO8062 09/112,809 IJ22 PO8034 09/112,780 IJ23 PO8039 09/113,083 IJ24 PO8041 09/113,121 IJ25 PO8004 09/113,122 IJ26 PO8037 09/112,793 IJ27 PO8043 09/112,794 IJ28 PO8042 09/113,128 IJ29 PO8064 09/113,127 IJ30 PO9389 09/112,756 IJ31 PO9391 09/112,755 IJ32 PP0888 09/112,754 IJ33 PP0891 09/112,811 IJ34 PP0890 09/112,812 IJ35 PP0873 09/112,813 IJ36 PP0993 09/112,814 IJ37 PP0890 09/112,764 IJ38 PP1398 09/112,765 IJ39 PP2592 09/112,767 IJ40 PP2593 09/112,768 IJ41 PP3991 09/112,807 IJ42 PP3987 09/112,806 IJ43 PP3985 09/112,820 IJ44 PP3983 09/112,821 IJ45 PO7935 09/112,822 IJM01 PO7936 09/112,825 IJM02 PO7937 09/112,826 IJM03 PO8061 09/112,827 IJM04 PO8054 09/112,828 IJM05 PO8065 6,071,750 IJM06 PO8055 09/113,108 IJM07 PO8053 09/113,109 IJM08 PO8078 09/113,123 IJM09 PO7933 09/113,114 IJM10 PO7950 09/113,115 IJM11 PO7949 09/113,129 IJM12 PO8060 09/113,124 IJM13 PO8059 09/113,125 IJM14 PO8073 09/113,126 IJM15 PO8076 09/113,119 IJM16 PO8075 09/113,120 IJM17 PO8079 09/113,221 IJM18 PO8050 09/113,116 IJM19 PO8052 09/113,118 IJM20 PO7948 09/113,117 IJM21 PO7951 09/113,113 IJM22 PO8074 09/113,130 IJM23 PO7941 09/113,110 IJM24 PO8077 09/113,112 IJM25 PO8058 09/113,087 IJM26 PO8051 09/113,074 IJM27 PO8045 6,111,754 IJM28 PO7952 09/113,088 IJM29 PO8046 09/112,771 IJM30 PO9390 09/112,769 IJM31 PO9392 09/112,770 IJM32 PP0889 09/112,798 IJM35 PP0887 09/112,801 IJM36 PP0882 09/112,800 IJM37 PP0874 09/112,799 IJM38 PP1396 09/113,098 IJM39 PP3989 09/112,833 IJM40 PP2591 09/112,832 IJM41 PP3990 09/112,831 IJM42 PP3986 09/112,830 IJM43 PP3984 09/112,836 IJM44 PP3982 09/112,835 IJM45 PP0895 09/113,102 IR01 PP0870 09/113,106 IR02 PP0869 09/113,105 IR04 PP0887 09/113,104 IR05 PP0885 09/112,810 IR06 PP0884 09/112,766 IR10 PP0886 09/113,085 IR12 PP0871 09/113,086 IR13 PP0876 09/113,094 IR14 PP0877 09/112,760 IR16 PP0878 09/112,773 IR17 PP0879 09/112,774 IR18 PP0883 09/112,775 IR19 PP0880 09/112,745 IR20 PP0881 09/113,092 IR21 PO8006 6,087,638 MEMS02 PO8007 09/113,093 MEMS03 PO8008 09/113,062 MEMS04 PO8010 6,041,600 MEMS05 PO8011 09/113,082 MEMS06 PO7947 6,067,797 MEMS07 PO7944 09/113,080 MEMS09 PO7946 6,044,646 MEMS10 PO9393 09/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 09/113,075 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to a micron electro-mechanical system for the ejection of fluids.

BACKGROUND OF THE INVENTION

In micro-electro mechanical systems (MEMS) it is often necessary to manipulate a fluid. The manipulation of a fluid can result in a clogging of a MEMS system, especially when the fluid contains contaminating bodies which clog fluid passage ways.

SUMMARY OF THE INVENTION

It is an object of the present invention to an integral structure with a MEMS device to filter out foreign bodies in an ink supply.

In accordance with a first aspect of the present invention there is provided a micro-electro mechanical system for controlling the flow of a liquid, this system being constructed in a planar form. The effect of impurities in the liquid is substantially removed by providing an integral grill structure in the path of the flow of the liquid. This serves to filter foreign bodies in the liquid. Preferably, the micro-electro mechanical system comprises an ink jet printing system and the grill forms one wall of a nozzle chamber for filtering ink entering the nozzle chamber. Further, the filter comprises substantially nitride.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a single ink jet nozzle constructed in accordance with the preferred embodiment.

FIG. 2 is a schematic cross-sectional view of a single ink jet nozzle constructed in accordance with the preferred embodiment, with the thermal actuator in its activated state.

FIG. 3 is a schematic diagram of the conductive layer utilized in the thermal actuator of the ink jet nozzle constructed in accordance with the preferred embodiment.

FIG. 4 is a close up perspective view of portion A of FIG. 3.

FIG. 5 is a cross-sectional schematic diagram illustrating the construction of a corrugated conductive layer in accordance with the preferred embodiment of the present invention.

FIG. 6 is a schematic cross-sectional diagram illustrating the development of a resist material through a half-toned mask utilized in the fabrication of a single ink jet nozzle in accordance with the preferred embodiment.

FIG. 7 is an exploded perspective view illustrating the construction of a single ink jet nozzle in accordance with the preferred embodiment.

FIG. 8 is a perspective view of a portion of an ink jet printhead having ink jet nozzles in accordance with the preferred embodiment.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

The preferred embodiment of the present invention will be discussed with reference to a fluid system which comprises an ink jet printing device wherein it is required to filter the ink supply so as to ensure the continual operation of the ink jet printer. The present invention should not necessarily be restricted to the field of ink jet printing, as will be readily evident.

In the preferred embodiment, there is provided an ink jet printer having ink ejection nozzles from which ink is ejected with the ink ejection being actuated by means of a thermal actuator which includes a “corrugated” copper heating element encased in a polytetrafluoroethylene (PTFE) layer.

Turning now to FIG. 1, there is illustrated a cross-sectional view of a single ink jet nozzle 10 in accordance with the present embodiment. The ink jet nozzle 10 includes an ink ejection port 11 for the ejection of ink from a chamber 12 by the actuation of a thermal paddle actuator 13. The thermal paddle actuator 13 comprises an inner copper heating portion 14 and a planar portion 15 which are encased in an outer PTFE layer 16. The outer PTFE layer 16 has an extremely high coefficient of thermal expansion (approximately 770×10⁻⁶, or around 380 times that of silicon). The PTFE layer 16 is also highly hydrophobic which results in an air bubble 17 being formed under the thermal actuator 13 due to out-gassing etc. The top PTFE layer is treated so as to make it hydrophilic. The heating portion 14 is also formed within the lower portion of the actuator 13.

The heater 14 is connected at ends 20,21 (see also FIG. 7) to a lower CMOS drive layer 18 containing drive circuitry (not shown). For the purposes of actuation of the actuator 13, a current is passed through the copper heating portion 14 which heats the bottom surface of the actuator 13. Turning now to FIG. 2, the bottom surface of the actuator 13, in contact with air bubble 17 remains heated while any top surface heating is carried away by the exposure of the top surface of the actuator 13 to the ink within the chamber 12. Hence, the bottom PTFE layer expands more rapidly resulting in a general rapid bending upwards of the actuator 13 (as illustrated in FIG. 2) which consequentially causes the ejection of ink from the ink ejection port 11. An air inlet channel 28 is formed between two nitride layers 42, 26 such that air is free to flow in the direction of an arrow 29 along a channel 28 and through holes 25, in accordance with any fluctuating pressure influences. The air flow acts to reduce the vacuum on the back surface of actuator 13 during operation. As a result less energy is required for the movement of the actuator 13.

The actuator 13 can be deactivated by turning off the current to the heating portion 14. This will result in a return of the actuator 13 to its rest position.

The thermal actuator 13 includes a number of significant features. In FIG. 3 there is illustrated a schematic diagram of the conductive layer of the thermal actuator 13. The conductive layer defines the planar portion 15, which can be constructed from the same material as the heating portion 14 copper, and which defines a series of holes 23. The holes 23 are provided for interconnecting layers of PTFE both above and below the planar portion 15 so as to resist any movement of the PTFE layers relative to the planar portion 15 and thereby reducing any opportunities for the delamination of the PTFE and copper layers.

Turning to FIG. 4, there is illustrated a close up view of the heating portion 14 illustrating corrugations 22 of the heating portion 14 within the PTFE. The corrugations 22 of the heater 14 allow for a rapid heating of portions of a bottom layer surrounding the corrugations 22. Any resistive heater which is based upon applying a current to heat an object will result in a rapid, substantially uniform elevation in temperature of the outer surface of the current carrying conductor. The surrounding PTFE volume is therefore heated by means of thermal conduction from the heating portion 14. This thermal conduction is known to proceed, to a first approximation, at a substantially linear rate with respect to distance from a resistive element. By utilizing the corrugations, the bottom surface of the actuator 13 is more rapidly heated as, on average, a greater volume of the bottom PTFE surface is closer to a portion of the resistive element. Therefore a rapid actuation of the actuator 13 results. Further, the corrugation 22 also assist in resisting any delamination of the copper and PTFE layer.

Turning now to FIG. 5, the corrugated resistive element can be formed by depositing a resist layer 50 on top of the first PTFE layer 51. The resist layer 50 is exposed utilizing a mask 52 having a half-tone pattern delineating the corrugations. After development the resist 50 contains the corrugation pattern. The resist layer 50 and the PTFE layer 51 are then etched utilizing an etchant that erodes the resist layer 50 at substantially the same rate as the PTFE layer 51. This transfers the corrugated pattern into the PTFE layer 51. Turning to FIG. 6, on top of the corrugated PTFE layer 51 is deposited the heating portion 14 which takes on a corrugated form in accordance with its under layer. The heating portion layer 14 is then etched in a serpentine or concertina form. Subsequently, a further PTFE layer 53 is deposited on top of the heating portion 14 so as to form the top layer of the thermal actuator 13. Finally, the second PTFE layer 52 is planarized to form the top surface of the thermal actuator 13 (FIG. 1).

Returning again now to FIG. 1, it is noted that an ink supply can be supplied through a throughway for channel 38 which can be constructed by means of deep anisotropic silicon trench etching such as that available from STS Limited (“Advanced Silicon Etching Using High Density Plasmas” by J. K. Bhardwaj, H. Ashraf, page 224 of Volume 2639 of the SPIE Proceedings in Micro Machining and Micro Fabrication Process Technology). The ink supply flows from channel 38 through spaced apart apertures 40 (see also FIG. 7) into chamber 12. The apertures 40 are defined between poles 241, forming a filter 341 (see FIG. 7). Importantly, the poles 241 which can comprise silicon nitride or similar insulating material act to remove foreign bodies from the ink flow. The poles 241 also help to pinch the PTFE actuator 13 to a base CMOS layer 18, the pinching providing an important assistance for the thermal actuator 13 so as to ensure a substantially decreased likelihood of the thermal actuator layer 13 separating from a base CMOS layer 18.

A series of sacrificial etchant holes 19 are defined in a top wall 48 of the chamber 12 to allow sacrificial etchant to enter the chamber 12 during fabrication so as to increase the rate of etching. The small size of the holes 19, does not affect the operation of the device 10 substantially as the surface tension across the holes 19 inhibit ink from being ejected from these holes, whereas the larger sized port 11 allows for the ejection of ink.

Turning now to FIG. 7, there is illustrated an exploded perspective view of a single nozzle 10. The nozzles 10 can be formed in layers starting with a silicon wafer substrate 41 having a CMOS layer 18 on top thereof as required. The CMOS layer 18 provides the various drive circuitry for driving the actuator 13.

On top of the CMOS layer 18 a nitride layer 42 is deposited, providing primarily protection for lower layers from corrosion or etching. Next a PTFE layer 26 is constructed having the aforementioned holes 25 (see FIG. 1), and posts 27 (see FIG. 1). The structure of the PTFE layer 26 can be formed by first laying down a sacrificial glass layer (not shown) onto which the PTFE layer 26 is deposited. The PTFE layer 26 includes various features, for example, a lower ridge portion 30 in addition to vias for subsequent material layers.

In construction of the actuator 13 (FIG. 1), the process of creating a first PTFE layer 60 proceeds by laying down a sacrificial layer on top of the layer 26 in which the air bubble 17, underneath the actuator 13 (FIG. 1), subsequently forms. On top of this is formed a first PTFE layer utilizing the relevant mask. Preferably, the PTFE layer includes vias for the subsequent copper interconnections. Next, a copper layer 43 is deposited on top of the first PTFE layer 60 and a subsequent PTFE layer 61 is deposited on top of the copper layer 43, in each case utilizing the required mask.

The nitride layer 46 can be formed by the utilization of a sacrificial glass layer which is masked and etched as required to form side walls and the filter 341. Subsequently, the top nitride layer 48 is deposited again utilizing the appropriate mask having considerable holes 19 as required. Subsequently, the various sacrificial layers can be etched away so as to release the structure of the thermal actuator.

In FIG. 8 there is illustrated a section of an ink jet printhead configuration 90 utilizing ink jet nozzles constructed in accordance with the preferred embodiment 91. The configuration 90 can be utilized in a three color process, 16 Oodpi printhead utilizing three sets of two rows of nozzle chambers 92,93, which are interconnected to one ink supply channel 94, for each set. The three supply channels 94, 95, 96 are interconnected to cyan colored, magenta colored and yellow colored ink reservoirs respectively. Ink is supplied through respective apertures 200, 202, 204 formed in the wafer substrate and extending through the wafer substrate 206 to the back surface thereof.

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal inkjet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal inkjet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric inkjet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per print head, but is a major impediment to the fabrication of pagewidth print heads with 19,200 nozzles.

Ideally, the inkjet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new inkjet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the inkjet systems described below with differing levels of difficulty. Forty-five different inkjet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table below.

The inkjet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems

For ease of manufacture using standard process equipment, the print head is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the print head is 100 mm long, with a width which depends upon the inkjet type. The smallest print head designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The print heads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the print head by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The print head is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 which matches the docket numbers in the in the table under the heading Cross References to Related Applications.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet print heads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a printer may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) Description Advantages Disadvantages Examples Thermal An electrothermal Large force High power Canon Bubblejet bubble heater heats the ink to generated Ink carrier limited to 1979 Endo et al GB above boiling point, Simple construction water patent 2,007,162 transferring significant No moving parts Low efficiency Xerox heater-in-pit heat to the aqueous Fast operation High temperatures 1990 Hawkins et al ink. A bubble Small chip area required U.S. Pat. No. 4,899,181 nucleates and quickly required for actuator High mechanical Hewlett-Packard TIJ forms, expelling the stress 1982 Vaught et al ink. Unusual materials U.S. Pat. No. 4,490,728 The efficiency of the required process is low, with Large drive typically less than transistors 0.05% of the electrical Cavitation causes energy being actuator failure transformed into Kogation reduces kinetic energy of the bubble formation drop. Large print heads are difficult to fabricate Piezo- A piezoelectric crystal Low power Very large area Kyser et al U.S. Pat. No. electric such as lead consumption required for actuator 3,946,398 lanthanum zirconate Many ink types can Difficult to integrate Zoltan U.S. Pat. No. (PZT) is electrically be used with electronics 3,683,212 activated, and either Fast operation High voltage drive 1973 Stemme U.S. Pat. No. expands, shears, or High efficiency transistors required 3,747,120 bends to apply Full pagewidth print Epson Stylus pressure to the ink, heads impractical Tektronix ejecting drops. due to actuator size IJ04 Requires electrical poling in high field strengths during manufacture Electro- An electric field is Low power Low maximum Seiko Epson, Usui strictive used to activate consumption strain (approx. et all JP 253401/96 electrostriction in Many ink types can 0.01%) IJ04 relaxor materials such be used Large area required as lead lanthanum Low thermal for actuator due to zirconate titanate expansion low strain (PLZT) or lead Electric field Response speed is magnesium niobate strength required marginal (˜10 μs) (PMN). (approx. 3.5 V/μm) High voltage drive can be generated transistors required without difficulty Full pagewidth print Does not require heads impractical electrical poling due to actuator size Ferro- An electric field is Low power Difficult to integrate IJ04 electric used to induce a phase consumption with electronics transition between the Many ink types can Unusual materials antiferroelectric (AFE) be used such as PLZSnT are and ferroelectric (FE) Fast operation required phase. Perovskite (<1 μs) Actuators require a materials such as tin Relatively high large area modified lead longitudinal strain lanthanum zirconate High efficiency titanate (PLZSnT) Electric field exhibit large strains of strength of around 3 up to 1% associated V/μm can be readily with the AFE to FE provided phase transition. Electro- Conductive plates are Low power Difficult to operate IJ02, IJ04 static separated by a consumption electrostatic devices plates compressible or fluid Many ink types can in an aqueous dielectric (usually air). be used environment Upon application of a Fast operation The electrostatic voltage, the plates actuator will attract each other and normally need to be displace ink, causing separated from the drop ejection. The ink conductive plates may Very large area be in a comb or required to achieve honeycomb structure, high forces or stacked to increase High voltage drive the surface area and transistors may be therefore the force. required Full pagewidth print heads are not competitive due to actuator size Electro- A strong electric field Low current High voltage 1989 Saito et al, static pull is applied to the ink, consumption required U.S. Pat. No. 4,799,068 on ink whereupon Low temperature May be damaged by 1989 Miura et al, electrostatic attraction sparks due to air U.S. Pat. No. 4,810,954 accelerates the ink breakdown Tone-jet towards the print Required field medium. strength increases as the drop size decreases High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet Low power Complex fabrication IJ07, IJ10 magnet directly attracts a consumption Permanent magnetic electro- permanent magnet, Many ink types can material such as magnetic displacing ink and be used Neodymium Iron causing drop ejection. Fast operation Boron (NdFeB) Rare earth magnets High efficiency required. with a field strength Easy extension from High local currents around 1 Tesla can be single nozzles to required used. Examples are: pagewidth print Copper metalization Samarium Cobalt heads should be used for (SaCo) and magnetic long materials in the electromigration neodymium iron boron lifetime and low family (NdFeB, resistivity NdDyFeBNb, Pigmented inks are NdDyFeB, etc) usually infeasible Operating temperature limited to the Curie temperature (around 540 K) Soft A solenoid induced a Low power Complex fabrication IJ01, IJ05, IJ08, magnetic magnetic field in a soft consumption Materials not IJ10, IJ12, IJ14, core magnetic core or yoke Many ink types can usually present in a IJ15, IJ17 electro- fabricated from a be used CMOS fab such as magnetic ferrous material such Fast operation NiFe, CoNiFe, or as electroplated iron High efficiency CoFe are required alloys such as CoNiFe Easy extension from High local currents [1], CoFe, or NiFe single nozzles to required alloys. Typically, the pagewidth print Copper metalization soft magnetic material heads should be used for is in two parts, which long are normally held electromigration apart by a spring. lifetime and low When the solenoid is resistivity actuated, the two parts Electroplating is attract, displacing the required ink. High saturation flux density is required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force acts as a IJ06, IJ11, IJ13, force acting on a current consumption twisting motion IJ16 carrying wire in a Many ink types can Typically, only a magnetic field is be used quarter of the utilized. Fast operation solenoid length This allows the High efficiency provides force in a magnetic field to be Easy extension from useful direction supplied externally to single nozzles to High local currents the print head, for pagewidth print required example with rare heads Copper metalization earth permanent should be used for magnets. long Only the current electromigration carrying wire need be lifetime and low fabricated on the print- resistivity head, simplifying Pigmented inks are materials usually infeasible requirements. Magneto- The actuator uses the Many ink types can Force acts as a Fischenbeck, U.S. Pat. No. striction giant magnetostrictive be used twisting motion 4,032,929 effect of materials Fast operation Unusual materials IJ25 such as Terfenol-D (an Easy extension from such as Terfenol-D alloy of terbium, single nozzles to are required dysprosium and iron pagewidth print High local currents developed at the Naval heads required Ordnance Laboratory, High force is Copper metalization hence Ter-Fe-NOL). available should be used for For best efficiency, the long actuator should be pre- electromigration stressed to approx. 8 lifetime and low MPa. resistivity Pre-stressing may be required Surface Ink under positive Low power Requires Silverbrook, EP tension pressure is held in a consumption supplementary force 0771 658 A2 and reduction nozzle by surface Simple construction to effect drop related patent tension. The surface No unusual separation applications tension of the ink is materials required in Requires special ink reduced below the fabrication surfactants bubble threshold, High efficiency Speed may be causing the ink to Easy extension from limited by surfactant egress from the single nozzles to properties nozzle. pagewidth print heads Viscosity The ink viscosity is Simple construction Requires Silverbrook, EP reduction locally reduced to No unusual supplementary force 0771 658 A2 and select which drops are materials required in to effect drop related patent to be ejected. A fabrication separation applications viscosity reduction can Easy extension from Requires special ink be achieved single nozzles to viscosity properties electrothermally with pagewidth print High speed is most inks, but special heads difficult to achieve inks can be engineered Requires oscillating for a 100:1 viscosity ink pressure reduction. A high temperature difference (typically 80 degrees) is required Acoustic An acoustic wave is Can operate without Complex drive 1993 Hadimioglu et generated and a nozzle plate circuitry al, EUP 550,192 focussed upon the Complex fabrication 1993 Elrod et al, drop ejection region. Low efficiency EUP 572,220 Poor control of drop position Poor control of drop volume Thermo- An actuator which Low power Efficient aqueous IJ03, IJ09, IJ17, elastic relies upon differential consumption operation requires a IJ18, IJ19, IJ20, bend thermal expansion Many ink types can thermal insulator on IJ21, IJ22, IJ23, actuator upon Joule heating is be used the hot side IJ24, IJ27, IJ28, used. Simple planar Corrosion IJ29, IJ30, IJ31, fabrication prevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35, IJ36, IJ37, required for each Pigmented inks may IJ38, IJ39, IJ40, actuator be infeasible, as IJ41 Fast operation pigment particles High efficiency may jam the bend CMOS compatible actuator voltages and currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a very High force can be Requires special IJ09, IJ17, IJ18, thermo- high coefficient of generated material (e.g. PTFE) IJ20, IJ21, IJ22, elastic thermal expansion Three methods of Requires a PTFE IJ23, IJ24, IJ27, actuator (CTE) such as PTFE deposition are deposition process, IJ28, IJ29, IJ30, polytetrafluoroethylene under development: which is not yet IJ31, IJ42, IJ43, (PTFE) is used. As chemical vapor standard in ULSI IJ44 high CTE materials deposition (CVD), fabs are usually non- spin coating, and PTFE deposition conductive, a heater evaporation cannot be followed fabricated from a PTFE is a candidate with high conductive material is for low dielectric temperature (above incorporated. A 50 μm constant insulation 350° C.) processing long PTFE bend in ULSI Pigmented inks may actuator with Very low power be infeasible, as polysilicon heater and consumption pigment particles 15 mW power input Many ink types can may jam the bend can provide 180 μN be used actuator force and 10 μm Simple planar deflection. Actuator fabrication motions include: Small chip area Bend required for each Push actuator Buckle Fast operation Rotate High efficiency CMOS compatible voltages and currents Easy extension from single nozzles to pagewidth print heads Conduct- A polymer with a high High force can be Requires special IJ24 ive coefficient of thermal generated materials polymer expansion (such as Very low power development (High thermo- PTFE) is doped with consumption CTE conductive elastic conducting substances Many ink types can polymer) actuator to increase its be used Requires a PTFE conductivity to about 3 Simple planar deposition process, orders of magnitude fabrication which is not yet below that of copper. Small chip area standard in ULSI The conducting required for each fabs polymer expands actuator PTFE deposition when resistively Fast operation cannot be followed heated. High efficiency with high Examples of CMOS compatible temperature (above conducting dopants voltages and 350° C.) processing include: currents Evaporation and Carbon nanotubes Easy extension from CVD deposition Metal fibers single nozzles to techniques cannot Conductive polymers pagewidth print be used such as doped heads Pigmented inks may polythiophene be infeasible, as Carbon granules pigment particles may jam the bend actuator Shape A shape memory alloy High force is Fatigue limits IJ26 memory such as TiNi (also available (stresses maximum number alloy known as Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy Large strain is Low strain (1%) is developed at the Naval available (more than required to extend Ordnance Laboratory) 3%) fatigue resistance is thermally switched High corrosion Cycle rate limited between its weak resistance by heat removal martensitic state and Simple construction Requires unusual its high stiffness Easy extension from materials (TiNi) austenic state. The single nozzles to The latent heat of shape of the actuator pagewidth print transformation must in its martensitic state heads be provided is deformed relative to Low voltage High current the austenic shape. operation operation The shape change Requires pre- causes ejection of a stressing to distort drop. the martensitic state Linear Linear magnetic Linear Magnetic Requires unusual IJ12 Magnetic actuators include the actuators can be semiconductor Actuator Linear Induction constructed with materials such as Actuator (LIA), Linear high thrust, long soft magnetic alloys Permanent Magnet travel, and high (e.g. CoNiFe) Synchronous Actuator efficiency using Some varieties also (LPMSA), Linear planar require permanent Reluctance semiconductor magnetic materials Synchronous Actuator fabrication such as Neodymium (LRSA), Linear techniques iron boron (NdFeB) Switched Reluctance Long actuator travel Requires complex Actuator (LSRA), and is available multi-phase drive the Linear Stepper Medium force is circuitry Actuator (LSA). available High current Low voltage operation operation

BASIC OPERATION MODE Description Advantages Disadvantages Examples Actuator This is the simplest Simple operation Drop repetition rate Thermal ink jet directly mode of operation: the No external fields is usually limited to Piezoelectric ink jet pushes ink actuator directly required around 10 kHz. IJ01, IJ02, IJ03, supplies sufficient Satellite drops can However, this is not IJ04, IJ05, IJ06, kinetic energy to expel be avoided if drop fundamental to the IJ07, IJ09, IJ11, the drop. The drop velocity is less than method, but is IJ12, IJ14, IJ16, must have a sufficient 4 m/s related to the refill IJ20, IJ22, IJ23, velocity to overcome Can be efficient, method normally IJ24, IJ25, IJ26, the surface tension. depending upon the used IJ27, IJ28, IJ29, actuator used All of the drop IJ30, IJ31, IJ32, kinetic energy must IJ33, IJ34, IJ35, be provided by the IJ36, IJ37, IJ38, actuator IJ39, IJ40, IJ41, Satellite drops IJ42, IJ43, IJ44 usually form if drop velocity is greater than 4.5 m/s Proximity The drops to be Very simple print Requires close Silverbrook, EP printed are selected by head fabrication can proximity between 0771 658 A2 and some manner (e.g. be used the print head and related patent thermally induced The drop selection the print media or applications surface tension means does not need transfer roller reduction of to provide the May require two pressurized ink). energy required to print heads printing Selected drops are separate the drop alternate rows of the separated from the ink from the nozzle image in the nozzle by Monolithic color contact with the print print heads are medium or a transfer difficult roller. Electro- The drops to be Very simple print Requires very high Silverbrook, EP static pull printed are selected by head fabrication can electrostatic field 0771 658 A2 and on ink some manner (e.g. be used Electrostatic field related patent thermally induced The drop selection for small nozzle applications surface tension means does not need sizes is above air Tone-Jet reduction of to provide the breakdown pressurized ink). energy required to Electrostatic field Selected drops are separate the drop may attract dust separated from the ink from the nozzle in the nozzle by a strong electric field. Magnetic The drops to be Very simple print Requires magnetic Silverbrook, EP pull on ink printed are selected by head fabrication can ink 0771 658 A2 and some manner (e.g. be used Ink colors other than related patent thermally induced The drop selection black are difficult applications surface tension means does not need Requires very high reduction of to provide the magnetic fields pressurized ink). energy required to Selected drops are separate the drop separated from the ink from the nozzle in the nozzle by a strong magnetic field acting on the magnetic ink. Shutter The actuator moves a High speed (>50 Moving parts are IJ13, IJ17, IJ21 shutter to block ink kHz) operation can required flow to the nozzle. The be achieved due to Requires ink ink pressure is pulsed reduced refill time pressure modulator at a multiple of the Drop timing can be Friction and wear drop ejection very accurate must be considered frequency. The actuator energy Stiction is possible can be very low Shuttered The actuator moves a Actuators with Moving parts are IJ08, IJ15, IJ18, grill shutter to block ink small travel can be required IJ19 flow through a grill to used Requires ink the nozzle. The shutter Actuators with pressure modulator movement need only small force can be Friction and wear be equal to the width used must be considered of the grill holes. High speed (>50 Stiction is possible kHz) operation can be achieved Pulsed A pulsed magnetic Extremely low Requires an external IJ10 magnetic field attracts an ‘ink energy operation is pulsed magnetic pull on ink pusher’ at the drop possible field pusher ejection frequency. An No heat dissipation Requires special actuator controls a problems materials for both catch, which prevents the actuator and the the ink pusher from ink pusher moving when a drop is Complex not to be ejected. construction

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description Advantages Disadvantages Examples None The actuator directly Simplicity of Drop ejection Most ink jets, fires the ink drop, and construction energy must be including there is no external Simplicity of supplied by piezoelectric and field or other operation individual nozzle thermal bubble. mechanism required. Small physical size actuator IJ01, IJ02, IJ03, IJ04, IJ05, IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The ink pressure Oscillating ink Requires external Silverbrook, EP ink oscillates, providing pressure can provide ink pressure 0771 658 A2 and pressure much of the drop a refill pulse, oscillator related patent (including ejection energy. The allowing higher Ink pressure phase applications acoustic actuator selects which operating speed and amplitude must IJ08, IJ13, IJ15, stimul- drops are to be fired The actuators may be carefully IJ17, IJ18, IJ19, ation) by selectively operate with much controlled IJ21 blocking or enabling lower energy Acoustic reflections nozzles. The ink Acouitic lenses can in the ink chamber pressure oscillation be used to focus the must be designed may be achieved by sound on the for vibrating the print nozzles head, or preferably by an actuator in the ink supply. Media The print head is Low power Precision assembly Silverbrook, EP proximity placed in close High accuracy required 0771 658 A2 and proximity to the print Simple print head Paper fibers may related patent medium. Selected construction cause problems applications drops protrude from Cannot print on the print head further rough substrates than unselected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer Drops are printed to a High accuracy Bulky Silverbrook, EP roller transfer roller instead Wide range of print Expensive 0771 658 A2 and of straight to the print substrates can be Complex related patent medium. A transfer used construction applications roller can also be used Ink can be dried on Tektronix hot melt for proximity drop the transfer roller piezoelectric ink jet separation. Any of the IJ series Electro- An electric field is Low power Field strength Silverbrook, EP static used to accelerate Simple print head required for 0771 658 A2 and selected drops towards Construction separation of small related patent the print medium. drops is near or applications above air Tone-Jet breakdown Direct A magnetic field is Low power Requires magnetic Silverbrook, EP magnetic used to accelerate Simple print head ink 0771 658 A2 and field selected drops of construction Requires strong related patent magnetic ink towards magnetic field applications the print medium. Cross The print head is Does not require Requires external IJ06, IJ16 magnetic placed in a constant magnetic materials magnet field magnetic field. The to be integrated in Current densities Lorenz force in a the print head may be high, current carrying wire manufacturing resulting in is used to move the process electromigration actuator. problems Pulsed A pulsed magnetic Very low power Complex print head IJ10 magnetic field is used to operation is possible construction field cyclically attract a Small print head Magnetic materials paddle, which pushes size required in print on the ink. A small head actuator moves a catch, which selectively prevents the paddle from moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description Advantages Disadvantages Examples None No actuator Operational Many actuator Thermal Bubble Ink mechanical simplicity mechanisms have jet amplification is used. insufficient travel, IJ01, IJ02, IJ06, The actuator directly or insufficient force, IJ07, IJ16, IJ25, drives the drop to efficiently drive IJ26 ejection process. the drop ejection process Differential An actuator material Provides greater High stresses are Piezoelectric expansion expands more on one travel in a reduced involved IJ03, IJ09, IJ17, bend side than on the other. print head area Care must be taken IJ18, IJ19, IJ20, actuator The expansion may be that the materials do IJ21, IJ22, IJ23, thermal, piezoelectric, not delaminate IJ24, IJ27, IJ29, magnetostrictive, or Residual bend IJ30, IJ31, IJ32, other mechanism. The resulting from high IJ33, IJ34, IJ35, bend actuator converts temperature or high IJ36, IJ37, IJ38, a high force low travel stress during IJ39, IJ42, IJ43, actuator mechanism to formation IJ44 high travel, lower force mechanism. Transient A trilayer bend Very good High stresses are IJ40, IJ41 bend actuator where the two temperature stability involved actuator outside layers are High speed, as a Care must be taken identical. This cancels new drop can be that the materials do bend due to ambient fired before heat not delaminate temperature and dissipates residual stress. The Cancels residual actuator only responds stress of formation to transient heating of one side or the other. Reverse The actuator loads a Better coupling to Fabrication IJ05, IJ11 spring spring. When the the ink complexity actuator is turned off, High stress in the the spring releases. spring This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator A series of thin Increased travel Increased Some piezoelectric stack actuators are stacked. Reduced drive fabrication ink jets This can be voltage complexity IJ04 appropriate where Increased possibility actuators require high of short circuits due electric field strength, to pinholes such as electrostatic and piezoelectric actuators. Multiple Multiple smaller Increases the force Actuator forces may IJ12, IJ13, IJ18, actuators actuators are used available from an not add linearly, IJ20, IJ22, IJ28, simultaneously to actuator reducing efficiency IJ42, IJ43 move the ink. Each Multiple actuators actuator need provide can be positioned to only a portion of the control ink flow force required. accurately Linear A linear spring is used Matches low travel Requires print head IJ15 Spring to transform a motion actuator with higher area for the spring with small travel and travel requirements high force into a Non-contact method longer travel, lower of motion force motion. transformation Coiled A bend actuator is Increases travel Generally restricted IJ17, IJ21, IJ34, actuator coiled to provide Reduces chip area to planar IJ35 greater travel in a Planar implementations reduced chip area. implementations are due to extreme relatively easy to fabrication difficulty fabricate. in other orientations. Flexure A bend actuator has a Simple means of Care must be taken IJ10, IJ19, IJ33 bend small region near the increasing travel of not to exceed the actuator fixture point, which a bend actuator elastic limit in the flexes much more flexure area readily than the Stress distribution is remainder of the very uneven actuator. The actuator Difficult to flexing is effectively accurately model converted from an with finite element even coiling to an analysis angular bend, resulting in greater travel of the actuator tip. Catch The actuator controls a Very low actuator Complex IJ10 small catch. The catch energy construction either enables or Very small actuator Requires external disables movement of size force an ink pusher that is Unsuitable for controlled in a bulk pigmented inks manner. Gears Gears can be used to Low force, low Moving parts are IJ13 increase travel at the travel actuators can required expense of duration. be used Several actuator Circular gears, rack Can be fabricated cycles are required and pinion, ratchets, using standard More complex drive and other gearing surface MEMS electronics methods can be used. processes Complex construction Friction, friction, and wear are possible Buckle A buckle plate can be Very fast movement Must stay within S. Hirata et al, “An plate used to change a slow achievable elastic limits of the Ink-jet Head Using actuator into a fast materials for long Diaphragm motion. It can also device life Microactuator”, convert a high force, High stresses Proc. IEEE MEMS, low travel actuator involved Feb. 1996, pp 418- into a high travel, Generally high 423. medium force motion. power requirement IJ18, IJ27 Tapered A tapered magnetic Linearizes the Complex IJ14 magnetic pole can increase magnetic construction pole travel at the expense force/distance curve of force. Lever A lever and fulcrum is Matches low travel High stress around IJ32, IJ36, IJ37 used to transform a actuator with higher the fulcrum motion with small travel requirements travel and high force Fulcrum area has no into a motion with linear movement, longer travel and and can be used for lower force. The lever a fluid seal can also reverse the direction of travel. Rotary The actuator is High mechanical Complex IJ28 impeller connected to a rotary advantage construction impeller. A small The ratio of force to Unsuitable for angular deflection of travel of the actuator pigmented inks the actuator results in can be matched to a rotation of the the nozzle impeller vanes, which requirements by push the ink against varying the number stationary vanes and of impeller vanes out of the nozzle. Acoustic A refractive or No moving parts Large area required 1993 Hadimioglu et lens diffractive (e.g. zone Only relevant for al, EUP 550,192 plate) acoustic lens is acoustic ink jets 1993 Elrod et al, used to concentrate EUP 572,220 sound waves. Sharp A sharp point is used Simple construction Difficult to fabricate Tone-jet conductive to concentrate an using standard VLSI point electrostatic field. processes for a surface ejecting ink- jet Only relevant for electrostatic ink jets

ACTUATOR MOTION Description Advantages Disadvantages Examples Volume The volume of the Simple construction High energy is Hewlett-Packard expansion actuator changes, in the case of typically required to Thermal Ink jet pushing the ink in all thermal ink jet achieve volume Canon Bubblejet directions. expansion. This leads to thermal stress, cavitation, and kogation in thermal ink jet implementations Linear, The actuator moves in Efficient coupling to High fabrication IJ01, IJ02, IJ04, normal to a direction normal to ink drops ejected complexity may be IJ07, IJ11, IJ14 chip the print head surface. normal to the required to achieve surface The nozzle is typically surface perpendicular in the line of motion movement. Parallel to The actuator moves Suitable for planar Fabrication IJ12, IJ13, IJ15, chip parallel to the print fabrication complexity IJ33, , IJ34, IJ35, surface head surface. Drop Friction IJ36 ejection may still be Stiction normal to the surface. Membrane An actuator with a The effective area of Fabrication 1982 Howkins U.S. Pat. No. push high force but small the actuator complexity 4,459,601 area is used to push a becomes the Actuator size stiff membrane that is membrane area Difficulty of in contact with the ink. integration in a VLSI process Rotary The actuator causes Rotary levers may Device complexity IJ05, IJ08, IJ13, the rotation of some be used to increase May have friction at IJ28 element, such a grill or travel a pivot point impeller Small chip area requirements Bend The actuator bends A very small change Requires the 1970 Kyser et al when energized. This in dimensions can actuator to be made U.S. Pat. No. 3,946,398 may be due to be converted to a from at least two 1973 Stemme U.S. Pat. No. differential thermal large motion. distinct layers, or to 3,747,120 expansion, have a thermal IJ03, IJ09, IJ10, piezoelectric difference across the IJ19, IJ23, IJ24, expansion, actuator IJ25, IJ29, IJ30, magnetostriction, or IJ31, IJ33, IJ34, other form of relative IJ35 dimensional change. Swivel The actuator swivels Allows operation Inefficient coupling IJ06 around a central pivot. where the net linear to the ink motion This motion is suitable force on the paddle where there are is zero opposite forces Small chip area applied to opposite requirements sides of the paddle, e.g. Lorenz force. Straighten The actuator is Can be used with Requires careful IJ26, IJ32 normally bent, and shape memory balance of stresses straightens when alloys where the to ensure that the energized. austenic phase is quiescent bend is planar accurate Double The actuator bends in One actuator can be Difficult to make IJ36, IJ37, IJ38 bend one direction when used to power two the drops ejected by one element is nozzles. both bend directions energized, and bends Reduced chip size. identical. the other way when Not sensitive to A small efficiency another element is ambient temperature loss compared to energized. equivalent single bend actuators. Shear Energizing the Can increase the Not readily 1985 Fishbeck U.S. Pat. No. actuator causes a shear effective travel of applicable to other 4,584,590 motion in the actuator piezoelectric actuator material. actuators mechanisms Radial The actuator squeezes Relatively easy to High force required 1970 Zoltan U.S. Pat. No. con- an ink reservoir, fabricate single Inefficient 3,683,212 striction forcing ink from a nozzles from glass Difficult to integrate constricted nozzle. tubing as with VLSI macroscopic processes structures Coil/ A coiled actuator Easy to fabricate as Difficult to fabricate IJ17, IJ21, IJ34, uncoil uncoils or coils more a planar VLSI for non-planar IJ35 tightly. The motion of process devices the free end of the Small area required, Poor out-of-plane actuator ejects the ink. therefore low cost stiffness Bow The actuator bows (or Can increase the Maximum travel is IJ16, IJ18, IJ27 buckles) in the middle speed of travel constrained when energized. Mechanically rigid High force required Push-Pull Two actuators control The structure is Not readily suitable IJ18 a shutter. One actuator pinned at both ends, for ink jets which pulls the shutter, and so has a high out-of- directly push the ink the other pushes it. plane rigidity Curl A set of actuators curl Good fluid flow to Design complexity IJ20, IJ42 inwards inwards to reduce the the region behind volume of ink that the actuator they enclose. increases efficiency Curl A set of actuators curl Relatively simple Relatively large IJ43 outwards outwards, pressurizing construction chip area ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes enclose High efficiency High fabrication IJ22 a volume of ink. These Small chip area complexity simultaneously rotate, Not suitable for reducing the volume pigmented inks between the vanes. Acoustic The actuator vibrates The actuator can be Large area required 1993 Hadimioglu et vibration at a high frequency. physically distant for efficient al, EUP 550,192 from the ink operation at useful 1993 Elrod et al, frequencies EUP 572,220 Acoustic coupling and crosstalk Complex drive circuitry Poor control of drop volume and position None In various ink jet No moving parts Various other Silverbrook, EP designs the actuator tradeoffs are 0771 658 A2 and does not move. required to related patent eliminate moving applications parts Tone-jet

NOZZLE REFILL METHOD Description Advantages Disadvantages Examples Surface This is the normal way Fabrication Low speed Thermal ink jet tension that ink jets are simplicity Surface tension Piezoelectric ink jet refilled. After the Operational force relatively IJ01-IJ07, IJ10-IJ14, actuator is energized, simplicity small compared to IJ16, IJ20, IJ22-IJ45 it typically returns actuator force rapidly to its normal Long refill time position. This rapid usually dominates return sucks in air the total repetition through the nozzle rate opening. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle High speed Requires common IJ08, IJ13, IJ15, oscillating chamber is provided at Low actuator ink pressure IJ17, IJ18, IJ19, ink a pressure that energy, as the oscillator IJ21 pressure oscillates at twice the actuator need only May not be suitable drop ejection open or close the for pigmented inks frequency. When a shutter, instead of drop is to be ejected, ejecting the ink drop the shutter is opened for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill After the main High speed, as the Requires two IJ09 actuator actuator has ejected a nozzle is actively independent drop a second (refill) refilled actuators per nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to prevent its return from emptying the chamber again. Positive The ink is held a slight High refill rate, Surface spill must Silverbrook, EP ink positive pressure. therefore a high be prevented 0771 658 A2 and pressure After the ink drop is drop repetition rate Highly hydrophobic related patent ejected, the nozzle is possible print head surfaces applications chamber fills quickly are required Alternative for:, as surface tension and IJ01-IJ07, IJ10-IJ14, ink pressure both IJ16, IJ20, IJ22-IJ45 operate to refill the nozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description Advantages Disadvantages Examples Long inlet The ink inlet channel Design simplicity Restricts refill rate Thermal ink jet channel to the nozzle chamber Operational May result in a Piezoelectric ink jet is made long and simplicity relatively large chip IJ42, IJ43 relatively narrow, Reduces crosstalk area relying on viscous Only partially drag to reduce inlet effective back-flow. Positive The ink is under a Drop selection and Requires a method Silverbrook, EP ink positive pressure, so separation forces (such as a nozzle 0771 658 A2 and pressure that in the quiescent can be reduced rim or effective related patent state some of the ink Fast refill time hydrophobizing, or applications drop already protrudes both) to prevent Possible operation from the nozzle. flooding of the of the following: This reduces the ejection surface of IJ01-IJ07, IJ09- pressure in the nozzle the print head. IJ12, IJ14, IJ16, chamber which is IJ20, IJ22, , IJ23- required to eject a IJ34, IJ36-IJ41, certain volume of ink. IJ44 The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more baffles The refill rate is not Design complexity HP Thermal Ink Jet are placed in the inlet as restricted as the May increase Tektronix ink flow. When the long inlet method. fabrication piezoelectric ink jet actuator is energized, Reduces crosstalk complexity (e.g. the rapid ink Tektronix hot melt movement creates Piezoelectric print eddies which restrict heads). the flow through the inlet. The slower refill process is unrestricted, and does not result in eddies. Flexible In this method recently Significantly Not applicable to Canon flap disclosed by Canon, reduces back-flow most ink jet restricts the expanding actuator for edge-shooter configurations inlet (bubble) pushes on a thermal ink jet Increased flexible flap that devices fabrication restricts the inlet. complexity Inelastic deformation of polymer flap results in creep over extended use Inlet filter A filter is located Additional Restricts refill rate IJ04, IJ12, IJ24, between the ink inlet advantage of ink May result in IJ27, IJ29, IJ30 and the nozzle filtration complex chamber. The filter Ink filter may be construction has a multitude of fabricated with no small holes or slots, additional process restricting ink flow. steps The filter also removes particles which may block the nozzle. Small inlet The ink inlet channel Design simplicity Restricts refill rate IJ02, IJ37, IJ44 compared to the nozzle chamber May result in a to nozzle has a substantially relatively large chip smaller cross section area than that of the nozzle, OnIy partially resulting in easier ink effective egress out of the nozzle than out of the inlet. Inlet A secondary actuator Increases speed of Requires separate IJ09 shutter controls the position of the ink-jet print refill actuator and a shutter, closing off head operation drive circuit the ink inlet when the main actuator is energized. The inlet is The method avoids the Back-flow problem Requires careful IJ01, IJ03, IJ05, located problem of inlet back- is eliminated design to minimize IJ06, IJ07, IJ10, behind the flow by arranging the the negative IJ11, IJ14, IJ16, ink- ink-pushing surface of pressure behind the IJ22, IJ23, IJ25, pushing the actuator between paddle IJ28, IJ31, IJ32, surface the inlet and the IJ33, IJ34, IJ35, nozzle. IJ36, IJ39, IJ40, IJ41 Part of the The actuator and a Significant Small increase in IJ07, IJ20, IJ26, actuator wall of the ink reductions in back- fabrication IJ38 moves to chamber are arranged flow can be complexity shut off so that the motion of achieved the inlet the actuator closes off Compact designs the inlet. possible Nozzle In some configurations Ink back-flow None related to ink Silverbrook, EP actuator of ink jet, there is no problem is back-flow on 0771 658 A2 and does not expansion or eliminated actuation related patent result in movement of an applications ink back- actuator which may Valve-jet flow cause ink back-flow Tone-jet through the inlet.

NOZZLE CLEARING METHOD Description Advantages Disadvantages Examples Normal All of the nozzles are No added May not be Most ink jet systems nozzle fired periodically, complexity on the sufficient to IJ01, IJ02, IJ03, firing before the ink has a print head displace dried ink IJ04, IJ05, IJ06, chance to dry. When IJ07, IJ09, IJ10, not in use the nozzles IJ11, IJ12, IJ14, are sealed (capped) IJ16, IJ20, IJ22, against air. IJ23, IJ24, IJ25, The nozzle firing is IJ26, IJ27, IJ28, usually performed IJ29, IJ30, IJ31, during a special IJ32, IJ33, IJ34, clearing cycle, after IJ36, IJ37, IJ38, first moving the print IJ39, IJ40,, IJ41, head to a cleaning IJ42, IJ43, IJ44,, station. IJ45 Extra In systems which heat Can be highly Requires higher Silverbrook, EP power to the ink, but do not boil effective if the drive voltage for 0771 658 A2 and ink heater it under normal heater is adjacent to clearing related patent situations, nozzle the nozzle May require larger applications clearing can be drive transistors achieved by over- powering the heater and boiling ink at the nozzle. Rapid The actuator is fired in Does not require Effectiveness May be used with: success- rapid succession. In extra drive circuits depends IJ0I, IJ02, IJ03, ion of some configurations, on the print head substantially upon IJ04, IJ05, IJ06, actuator this may cause heat Can be readily the configuration of IJ07, IJ09, IJ10, pulses build-up at the nozzle controlled and the ink jet nozzle IJ11, IJ14, IJ16, which boils the ink, initiated by digital IJ20, IJ22, IJ23, clearing the nozzle. In logic IJ24, IJ25, IJ27, other situations, it may IJ28, IJ29, IJ30, cause sufficient IJ31, IJ32, IJ33, vibrations to dislodge IJ34, IJ36, IJ37, clogged nozzles. IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, IJ45 Extra Where an actuator is A simple solution Not suitable where May be used with: power to not normally driven to where applicable there is a hard limit IJ03, IJ09, IJ16, ink the limit of its motion, to actuator IJ20, IJ23, IJ24, pushing nozzle clearing may be movement IJ25, IJ27, IJ29, actuator assisted by providing IJ30, IJ31, IJ32, an enhanced drive IJ39, IJ40, IJ41, signal to the actuator. IJ42, IJ43, IJ44, IJ45 Acoustic An ultrasonic wave is A high nozzle High IJ08, IJ13, IJ15, resonance applied to the ink clearing capability implementation cost IJ17, IJ18, IJ19, chamber. This wave is can be achieved if system does not IJ21 of an appropriate May be already include an amplitude and implemented at very acoustic actuator frequency to cause low cost in systems sufficient force at the which already nozzle to clear include acoustic blockages. This is actuators easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle A microfabricated Can clear severely Accurate Silverbrook, EP clearing plate is pushed against clogged nozzles mechanical 0771 658 A2 and plate the nozzles. The plate alignment is related patent has a post for every required applications nozzle. A post moves Moving parts are through each nozzle, required displacing dried ink. There is risk of damage to the nozzles Accurate fabrication is required Ink The pressure of the ink May be effective Requires pressure May be used with pressure is temporarily where other pump or other all IJ series ink jets pulse increased so that ink methods cannot be pressure actuator streams from all of the used Expensive nozzles. This may be Wasteful of ink used in conjunction with actuator energizing. Print head A flexible ‘blade’ is Effective for planar Difficult to use if Many ink jet wiper wiped across the print print head surfaces print head surface is systems head surface. The Low cost non-planar or very blade is usually fragile fabricated from a Requires flexible polymer, e.g. mechanical parts rubber or synthetic Blade can wear out elastomer. in high volume print systems Separate A separate heater is Can be effective Fabrication Can be used with ink boiling provided at the nozzle where other nozzle complexity many IJ series ink heater although the normal clearing methods jets drop e-ection cannot be used mechanism does not Can be implemented require it. The heaters at no additional cost do not require in some ink jet individual drive configurations circuits, as many nozzles can be cleared simultaneously, and no imaging is required

NOZZLE PLATE CONSTRUCTION Description Advantages Disadvantages Examples Electro- A nozzle plate is Fabrication High temperatures Hewlett Packard formed separately fabricated simplicity and pressures are Thermal Ink jet nickel from electroformed required to bond nickel, and bonded to nozzle plate the print head chip. Minimum thickness constraints Differential thermal expansion Laser Individual nozzle No masks required Each hole must be Canon Bubblejet ablated or holes are ablated by an Can be quite fast individually formed 1988 Sercel et al., drilled intense UV laser in a Some control over Special equipment SPIE, Vol. 998 polymer nozzle plate, which is nozzle profile is required Excimer Beam typically a polymer possible Slow where there Applications, pp. such as polyimide or Equipment required are many thousands 76-83 polysulphone is relatively low cost of nozzles per print 1993 Watanabe et head al., U.S. Pat. No. 5,208,604 May produce thin burrs at exit holes Silicon A separate nozzle High accuracy is Two part K. Bean, IEEE micro- plate is attainable construction Transactions on machined micromachined from High cost Electron Devices, single crystal silicon, Requires precision Vol. ED-25, No. 10, and bonded to the alignment 1978, pp 1185-1195 print head wafer. Nozzles may be Xerox 1990 clogged by adhesive Hawkins et al., U.S. Pat. No. 4,899,181 Glass Fine glass capillaries No expensive Very small nozzle 1970 Zoltan U.S. Pat. No. capillaries are drawn from glass equipment required sizes are difficult to 3,683,212 tubing. This method Simple to make form has been used for single nozzles Not suited for mass making individual production nozzles, but is difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is High accuracy (<1 Requires sacrificial Silverbrook, EP surface deposited as a layer μm) layer under the 0771 658 A2 and micro- using standard VLSI Monolithic nozzle plate to form related patent machined deposition techniques. Low cost the nozzle chamber applications using VLSI Nozzles are etched in Existing processes Surface may be IJ01, IJ02, IJ04, litho- the nozzle plate using can be used fragile to the touch IJ11, IJ12, IJ17, graphic VLSI lithography and IJ18, IJ20, IJ22, processes etching. IJ24, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a High accuracy (<1 Requires long etch IJ03, IJ05, IJ06, etched buried etch stop in the μm) times IJ07, IJ08, IJ09, through wafer. Nozzle Monolithic Requires a support IJ10, IJ13, IJ14, substrate chambers are etched in Low cost wafer IJ15, IJ16, IJ19, the front of the wafer, No differential IJ21, IJ23, IJ25, and the wafer is expansion IJ26 thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle Various methods have No nozzles to Difficult to control Ricoh 1995 Sekiya et al plate been tried to eliminate become clogged drop position U.S. Pat. No. 5,412,413 the nozzles entirely, to accurately 1993 Hadimioglu et prevent nozzle Crosstalk problems al EUP 550,192 clogging. These 1993 Elrod et al include thermal bubble EUP 572,220 mechanisms and acoustic lens mechanisms Trough Each drop ejector has Reduced Drop firing IJ35 a trough through manufacturing direction is sensitive which a paddle moves. complexity to wicking. There is no nozzle Monolithic plate. Nozzle slit The elimination of No nozzles to Difficult to control 1989 Saito et al instead of nozzle holes and become clogged drop position U.S. Pat. No. 4,799,068 individual replacement by a slit accurately nozzles encompassing many Crosstalk problems actuator positions reduces nozzle clogging, but increases crosstalk due to ink surface waves

DROP EJECTION DIRECTION Description Advantages Disadvantages Examples Edge Ink flow is along the Simple construction Nozzles limited to Canon Bubblejet (‘edge surface of the chip, No silicon etching edge 1979 Endo et al GB shooter’) and ink drops are required High resolution is patent 2,007,162 ejected from the chip Good heat sinking difficult Xerox heater-in-pit edge. via substrate Fast color printing 1990 Hawkins et al Mechanically strong requires one print U.S. Pat. No. 4,899,181 Ease of chip head per color Tone-jet handing Surface Ink flow is along the No bulk silicon Maximum ink flow Hewlett-Packard TIJ (‘roof surface of the chip, etching required is severely restricted 1982 Vaught et al shooter’) and ink drops are Silicon can make an U.S. Pat. No. 4,490,728 ejected from the chip effective heat sink IJ02, IJ11, IJ12, surface, normal to the Mechanical strength IJ20, IJ22 plane of the chip. Through Ink flow is through the High ink flow Requires bulk Silverbrook, EP chip, chip, and ink drops are Suitable for silicon etching 0771 658 A2 and forward ejected from the front pagewidth print related patent (‘up surface of the chip. heads applications shooter’) High nozzle packing IJ04, IJ17, IJ18, density therefore IJ24, IJ27-IJ45 low manufacturing cost Through Ink flow is through the High ink flow Requires wafer IJ01, IJ03, IJ05, chip, chip, and ink drops are Suitable for thinning IJ06, IJ07, IJ08, reverse ejected from the rear pagewidth print Requires special IJ09, IJ10, IJ13, (‘down surface of the chip. heads handling during IJ14, IJ15, IJ16, shooter’) High nozzle packing manufacture IJ19, IJ21, IJ23, density therefore IJ25, IJ26 low manufacturing cost Through Ink flow is through the Suitable for Pagewidth print Epson Stylus actuator actuator, which is not piezoelectric print heads require Tektronix hot melt fabricated as part of heads several thousand piezoelectric ink jets the same substrate as connections to drive the drive transistors. circuits Cannot be manufactured in standard CMOS fabs Complex assembly required

INK TYPE Description Advantages Disadvantages Examples Aqueous, Water based ink which Environmentally Slow drying Most existing ink dye typically contains: friendly Corrosive jets water, dye, surfactant, No odor Bleeds on paper All IJ series ink humectant, and May jets biocide. strikethrough Silverbrook, EP Modern ink dyes have Cockles paper 0771 658 A2 and high water-fastness, related patent light fastness applications Aqueous, Water based ink which Environmentally Slow drying IJ02, IJ04, IJ21, pigment typically contains: friendly Corrosive IJ26, IJ27, IJ30 water, pigment, No odor Pigment may Silverbrook, EP surfactant, humectant, Reduced bleed clog nozzles 0771 658 A2 and and biocide. Reduced wicking Pigment may related patent Pigments have an Reduced clog actuator applications advantage in reduced strikethrough mechanisms Piezoelectric ink- bleed, wicking and Cockles paper jets. strikethrough. Thermal ink jets (with significant restrictions) Methyl MEK is a highly Very fast drying Odorous All IJ series ink Ethyl volatile solvent used Prints on various Flammable jets Ketone for industrial printing substrates such as (MEK) on difficult surfaces metals and plastics such as aluminum cans. Alcohol Alcohol based inks Fast drying Slight odor All IJ series ink (ethanol, can be used where the Operates at sub- Flammable jets 2-butanol, printer must operate at freezing and others) temperatures below temperatures the freezing point of Reduced paper water. An example of cockle this is in-camera Low cost consumer photographic printing. Phase The ink is solid at No drying time- High viscosity Tektronix hot change room temperature, and ink instantly freezes Printed ink melt piezoelectric (hot melt) is melted in the print on the print medium typically has a ink jets head before jetting. Almost any print ‘waxy’ feel 1989 Nowak U.S. Hot melt inks are medium can be used Printed pages Pat. No. 4,820,346 usually wax based, No paper cockle may ‘block’ All IJ series ink with a melting point occurs Ink temperature jets around 80° C. After No wicking may be above the jetting the ink freezes occurs curie point of almost instantly upon No bleed occurs permanent magnets contacting the print No strikethrough Ink heaters medium or a transfer occurs consume power roller. Long warm-up time Oil Oil based inks are High solubility High viscosity: All IJ series ink extensively used in medium for some this is a significant jets offset printing. They dyes limitation for use in have advantages in Does not cockle ink jets, which improved paper usually require a characteristics on Does not wick low viscosity. Some paper (especially no through paper short chain and wicking or cockle). multi-branched oils Oil soluble dies and have a sufficiently pigments are required. low viscosity. Slow drying Micro- A microemulsion is a Stops ink bleed Viscosity higher All IJ series ink emulsion stable, self forming High dye than water jets emulsion of oil, water, solubility Cost is slightly and surfactant. The Water, oil, and higher than water characteristic drop size amphiphilic soluble based ink is less than 100 nm, dies can be used High surfactant and is determined by Can stabilize concentration the preferred curvature pigment required (around of the surfactant. suspensions 5%) 

What is claimed is:
 1. A monolithic micro-mechanical system for the ejection of fluid, said system comprising: a wafer substrate; a series of nozzle chambers formed on said wafer substrate, each nozzle chamber comprising an ink ejection port formed in a first wall of said each nozzle for, in use, ejection of the ink, and each nozzle chamber further comprising grill apertures formed in a second wall of said each nozzle chamber, said grill apertures being oriented substantially perpendicularly with respect to said wafer substrate; and a fluid supply for supplying fluid to each of said nozzle chambers, said spaced apart grill apertures forming filters between said nozzle chambers and said fluid supply.
 2. A system as claimed in claim 1 wherein said nozzle chambers each include a thermal bend actuator attached at a first end to said substrate and having a second moveable end located away from said spaced apart poles, said moveable end being actuable to cause the ejection of said ink from said nozzle chambers, said grill apertures being formed in said second wall adjacent to the attachment of said actuator to said substrate.
 3. A system as claimed in claim 1, wherein each nozzle chamber comprises a series of spaced apart poles formed in the s econd wall of said each nozzle chamber defining said grill apertures, the poles being oriented substantially perpendicularly with respect to the substrate.
 4. A system as claimed in claim 3 wherein said poles a re formed from silicon nitride.
 5. A system as claimed in claim 1, wherein said nozzle chambers are formed by a deposition and etching process carried out on said wafer substrate.
 6. A monolithic micro-mechanical system for the ejection of fluid, said system comprising: a wafer substrate; a series of nozzle chambers formed on said wafer substrate, each nozzle chamber comprising a nozzle aperture formed in a first wall of said each nozzle chamber for, in use, ejection of the fluid, and each nozzle chamber further comprising grill apertures formed in a second wall of said each nozzle chamber; said grill apertures being of substantially uniform cross-section along a thickness of the second wall; and a fluid supply for supplying fluid to each of said nozzle chambers, said grill apertures forming a filter between said nozzle chambers and said fluid supply.
 7. A system as claimed in claim 6, wherein a thickness of said second wall is approximately five microns thick.
 8. A monolithic micro-mechanical system for the ejection of fluid, said system comprising a wafer substrate; a number of nozzle chamber side walls and roof walls formed on said wafer substrate by deposition and etching techniques, to define a plurality of nozzle chambers with an ejection port defined in each roof wall, and the nozzle chamber side walls and the roof walls defining an inlet to each nozzle chamber; and a plurality of actuators, each actuator being positioned within a respective nozzle chamber to eject ink from the respective ejection ports, wherein a plurality of elongate poles are arranged in a spaced, side-by-side manner, within each inlet to define a grill positioned within the inlet, the poles extending substantially orthogonally with respect to the wafer substrate.
 9. A system as claimed in claim 8, in which the poles within each inlet are configured to pinch the thermal actuator to the wafer substrate to decrease the likelihood of the actuator becoming separated from the wafer substrate.
 10. A system as claimed in claim 8, in which the nozzle chamber side walls, roof walls and poles are of silicon nitride.
 11. A monolithic micro-mechanical system for the ejection of fluid, said system comprising a wafer substrate; a number of nozzle chamber side walls and roof walls formed on said wafer substrate by deposition and etching techniques, to define a plurality of nozzle chambers with an ejection port defined in each roof wall, and the nozzle chamber side walls and the roof walls defining an inlet to each nozzle chamber; and a plurality of actuators, each actuator being positioned within a respective nozzle chamber to eject ink from the respective ejection ports, wherein a plurality of elongate poles are arranged in a spaced, side-by-side manner, within each inlet to define a grill positioned within the inlet, the poles extending substantially orthogonally with respect to the wafer substrate; further wherein the system includes three ink supply channels and the nozzle chambers are divided into three sets of two rows of nozzle chambers, each set of nozzle chambers being in fluid communication with one ink supply channel, so that a differently colored ink can be supplied to each set of nozzle chambers, via the respective ink supply channels. 